How the calculators work, and every test

The order we apply the rules

1. Inherited property, farmland, business premises and the 2023 weather event sales are excluded first (IR1229 pp2, 24 to 28).
2. The sale agreement date picks the rules: on or after 1 July 2024, the 2-year test; before that, the period set by the purchase agreement date (IR1229 p6, IR1227 p6).
3. The period runs from the title registration date (the purchase agreement date for off the plans) to the sale agreement date. The sale is inside if the sale agreement is before the anniversary.
4. If it was your main home, we test the land area and the days, ignoring construction, and apply the limits. For older sales of property acquired on or after 27 March 2021, we apportion as IR1227 shows.
5. Gain is the sale price less the purchase price, purchase costs, capital improvements, selling costs and the holding costs you enter, times your ownership share.
6. Tax is the difference between income tax on your other income plus the gain and income tax on your other income alone, for the tax year of settlement, using the shared IRD-tested brackets from Tax Calculator NZ.

Counting days and dates

We count days including both the first and the last day, which matches most IRD examples (Ari 590 days, Amelia 272, Zoe 1,096). IRD’s Mel example counts one day fewer; no example’s outcome changes. Dates are handled as calendar dates in UTC, so results never depend on your time zone. A 29 February start date reaches its anniversary on 1 March in a year without 29 February (our assumption).

The anniversary day

Neither IRD guide says what happens to a sale agreement signed exactly on the anniversary of the start date. IR1229 p39 says “taxable if sold before” the anniversary, so we treat the anniversary as outside the period, flag it in the result, and suggest signing a day later to be safe.

What the calculators do not model

• Other non-standard start dates (subdivided or partitioned land, perpetual leases, nominees, trustee changes, land overseas): enter the start date IR1229 p8 gives for your case.
• Different main homes for each co-owner, and the trust rules for main homes.
• The qualifying new build test itself (code compliance certificate dates): you tell us if it applies. It only matters for sales before 1 July 2024.
• Depreciation recovery, residential land withholding tax, GST, and tax rates for companies and trusts: we use individual rates.
• The intention test, dealer rules, shares, FIF and crypto are covered by the checker as likely outcomes, not calculated.